T last they were about to see this famous gas, oxygen,
this king of elements that in the past few days had
again and again been referred to by Uncle Paul in his
talks, but always wrapped in the mystery that enshrouds
the unknown. Now it was to be released from its
imprisonment in the chlorate of potash and subjected to
tests that promised to be interesting. Emile even
dreamed about it in the night, so much had his mind
dwelt on this gas that makes things burn. In his dreams
he saw the glass balloon and the bent tube cutting up
all sorts of silly capers on the circular edge of the
brazier, while the irascible chlorate and its comrade,
the dioxid, looked on curiously through the glass walls
of their prison. In the presence of the real things
about which he had dreamed the night
before—confronting, that is, the various
preparations for the coming experiment—the boy
was moved to fresh laughter when his uncle put the
balloon in place over the live coals.
They had not long to wait. Before it seemed possible
that the heat could have had time to act, and with no
visible change in the contents of the balloon, the
water in the bowl began to bubble at
 the end of the tube, a sure sign that gas was being set
free. The support already made from the bottom of a
flower-pot was arranged in position in the bowl
of water, and a large bottle of two or three liters'
capacity and with a wide mouth was filled brimming full
of water, stopped with the palm of the hand, and turned
upside down on the support. Emile steadied it with his
hand. The gas passed through the hole in the middle of
the support, and rose through the water in a tumultuous
and uninterrupted series of big bubbles, so that in a
few moments the bottle was filled with the gas that had
displaced the water. Then Uncle Paul took a tumbler,
plunged it into the bowl, and in this glass of water
set the mouth of the bottle, of course without letting
it come out into the air and lose any of the imprisoned
oxygen. That done, the bottle, standing upside down in
the glass of water, which served to exclude the air
from outside, was set safely away in a corner of the
room to wait until it was needed for some experiment
still to come. A second bottle took its place in the
bowl, was filled with gas in the same way, and set
aside for future use, after which a third and then a
fourth went through the same operation. The supply of
oxygen in the balloon seemed inexhaustible.
"There seems to be a lot of oxygen in a handful
 of chlorate," remarked Emile, surprised at the quantity
of gas being released.
"Yes, it is no small amount, as you see, for our four
bottles hold almost a dozen liters, taken together."
"And those dozen liters of oxygen were all in that
little heap of chlorate?"
"All were in the small amount of chlorate used. Was n't
I right in calling this salt a rich storehouse? The
chlorate is more than abundantly fed with oxygen; it
is crammed to the limit. The gas taken captive by
chemical combination is compressed in great quantities
into very small bulk. But all is not over yet; I hope
to fill this bottle, too."
Therewith Uncle Paul placed on the support in the bowl
an odd-looking, elongated bottle that had hardly
any neck, being of nearly the same width at top and
bottom. He did not say where it came from, but his
nephews thought they recognized it as an old
pickle-jar. They were smiling at seeing this
homely utensil pressed into such serious service, when
their uncle resumed his talk.
"Does my tall jar make you laugh? Because it once held
pickles, do you think it unworthy now to hold oxygen?
Away with such false pride, my lads! Let us use the
things at hand and not sigh for expensive luxuries. But
for this once we will carry out our program in a worthy
manner, just as we should if we had a
better-equipped laboratory at our disposal.
"Here is something that chemists call a gage. It is a
tall glass cylinder with a base to stand on.
 I proceed to fill it with oxygen while there is still
some left in the balloon, and we see that the gas
enters slowly, the supply being nearly exhausted. In
the balloon, the contents of which show no change in
appearance, there is left the dioxid of manganese just
as it was when I put it there. It has suffered neither
loss not gain, but it has promoted the decomposition of
the chlorate by enabling the heat to act upon it
evenly. The balloon itself, too, remains uninjured and
ready for further use when needed. As to the chlorate,
it has now lost all its oxygen, and is thus changed to
that white substance we saw yesterday remaining on the
embers after we had thrown on a pinch of chlorate and
watched it quicken the fire. In short, it has turned
into chlorid of potassium. So much for that. Now let us
put our supply of oxygen to some use, beginning with
that in the gage."
Carried from the bowl to the table with the usual
precautions—that is, being first closed with the
palm of the hand while still standing upside down in
the water—the gage was set upright on its base
and covered with a piece of glass pending certain
preparations consisting of fastening a short piece of
candle to an iron wire, as had been done before in the
experiment with nitrogen. Uncle Paul lighted the
candle, allowed the flame to get bright and full, and
then blew it out; but the wick was still glowing from
the combustion that had been so suddenly arrested.
"The candle which I have just blown out," said he, "but
which still shows a rod glow at the end
 of the wick, I am going to lower into the oxygen in the
gage. What will happen? We shall see."
Removing the piece of glass, he suited the action to
the word. Piff ! A slight explosion was heard
and the candle, relighting itself unaided, burned with
radiant brilliance. It was extinguished once more, the
wick still retaining its glowing spark, and lowered
again into the gage of oxygen. Another piff! and
the flame reappeared, burning with remarkable
brightness. Again and again, with care to leave the
wick slightly aglow, the candle, extinguished with a
breath, quickly relighted itself when it was lowered
into the oxygen. Each time a little explosion preceded
the revival of the flame. Emile clapped his hands with
delight at this repeated renewal of the flame, always
so prompt and so complete.
"How different it was with nitrogen, the partner of
oxygen in the air we breathe," he observed. "Oxygen
relights all of a sudden what is just about to stop
burning altogether, but nitrogen puts out what is
already well on fire. Could n't I try my hand at this
fine experiment, Uncle?"
"Surely; why not? But I must inform you that the
oxygen in the gage is by this time nearly exhausted,
the candle having used up a little every time it was
"But there's plenty more in those four bottles."
"I am keeping that for other experiments of still
"What shall I do, then?"
"You must content yourself with my old
pickle-  jar that I took the pains to fill with oxygen, counting
on it to take the place of a regular gage."
"I'll do that and be glad to."
"A wise decision, for the old pickle-jar will
render you yeoman service. My chief reason for using it
is to show you, by adding example to example, that
instructive experiments are possible even with the
commonest utensils. Our gage here is a luxury, an
unheard-of extravagance in our little village.
Almost any kind of bottle, any caper- or
pickle-jar, provided only it has a wide mouth to
admit the candle, would serve very well in performing
the striking experiment you now wish to repeat. All
right, then; you shall repeat it."
The jar being placed on the table, Emile began the
lighting and relighting of the candle, blowing it out
and rekindling the flame again and again. The
experiment had not gone better even with the regular
"There, now," said his uncle, "does n't my
pickle-jar answer the purpose admirably?"
"It is the contents and not the container that we
should give our attention to. If we supply it with
oxygen the candle will relight itself, no matter what
the oxygen is in, whether the chemist's gage or the
paltry pickle-bottle. As a close to the
experiment, leave the candle in the jar to burn as long
as it can. You will see how fast it will be used up."
And, indeed, the candle, immersed in oxygen, did not
fail to burn with devouring rapidity. It showed no
longer the calm flame that is maintained in
ordi-  nary air, but a furious tongue of fire, extraordinarily
bright and excessively hot, making the wax melt and run
down in big drops. The substance of the candle was
literally devoured rather than burned, and it was
evident that in a few minutes there would be consumed
in this energetic gas enough wax to last an hour in
atmospheric air. Finally the flame died down for lack
of oxygen, and Uncle Paul resumed his talk.
"Before continuing these spectacular experiments with
oxygen," said he, "let us quiet our emotions with a
little interlude. You know the characteristics that
enable us to recognize an acid,—first the sour
taste, and then the property of turning blue flowers
red. But it is not always practicable to test an acid
by the sense of taste, the flavor sometimes being very
weak or even quite imperceptible. The test with blue
flowers is a better one. But, unfortunately, violets
and other blue flowers redden with some difficulty when
the acid is weak. Chemistry has found the blue coloring
matter of lichens more easily affected. You know those
peculiar growths that look like flaky crusts on the
bark of trees and even on the surface of the hardest
rocks. They are of vegetable origin, and are called
lichens. One species found on rocks near the sea
furnishes a blue substance called litmus. The druggist
has this for sale in the form of little cubes,
ashy-blue in color and known as litmus tablets.
If you dissolve one of these in a little water, you
obtain a pale violet-blue liquid called tincture
"This tincture is one of the most convenient
for applying to acids, as it reddens much more
easily than do blue flowers. To illustrate, I pour into
this glass two fingers of the litmus tincture; then I
dip the end of a glass tube or of a common straw into
the acid in this bottle, an acid I have already
referred to as derived from sulphur,—sulphuric
acid, in fact. I do not dip it deeply, but merely touch
it to the liquid, and with this barely moistened straw
I stir the blue tincture, which immediately turns red
in proof (if I did not already know it) that what my
bottle contains is an acid."
"If the tincture of litmus is turned red by an acid,"
said Jules, "it ought to be turned green by a soluble
oxide, just as violets are; and so it would help us to
find out whether a thing was an oxid or not."
"It is perfectly natural to expect that, after seeing
what happens to blue flowers; and yet it is not the
case. Lime and other soluble oxids do not turn the blue
of litmus green, but leave it unchanged. However, this
lack is atoned for by another characteristic. Once
reddened by an acid, litmus is turned blue again by
means of a soluble oxid. Into the contents of this
glass, just now changed from blue to red by the
addition of sulphuric acid, I drop a tiny particle of
lime, and the liquid returns to its original blue. A
second time I apply a trace of the acid with the end of
this straw, and a second time the tincture turns red.
 applied in its turn once more, the blue color
reappears. These changes from blue to red and from red
to blue might be repeated indefinitely. Here we have,
then, a perfect test for determining whether a
substance is an acid or an oxid, provided only, of
course, that it is soluble in water. Wherever reddens
the blue tincture of litmus is an acid, and what
restores its blue to the tincture previously reddened
by acid is an oxid.
"If we had no litmus—and the lack of it would be
no great matter—we should have to be contented
with blue flowers. A bunch of violets would first be
crushed and stirred in water, and the bluish liquid
thus obtained would be strained and set aside to serve
the purpose of litmus. But it would show a difference
in one respect; though acids would turn it red, oxids
would not turn it blue again, but green; and of course
the blue liquid would turn green immediately when acted
upon by an oxid, without having to be previously
reddened by an acid. It is to be noted, further, that
weak acids might not be able to change the blue of
violets to red, and therefore litmus preferable as a
"Our interlude is over and we will go on with the
performance. We are going to burn several substances in
oxygen and watch their manner of burning. First comes
"Adopting the method you saw employed when we tried in
vain to make phosphorus and sulphur burn in a bottle
filled with nitrogen, I make a little cup out of a bit
of broken earthenware, and bend the end of an iron wire
into a circle for holding this
 cup. The iron wire is then passed through a large cork
stopper that will serve to hold it in place in the
bottle rather than to stop up the bottle itself. Hence
it does not matter much if the cork is too large for
the bottle. A small disk of stout cardboard laid over
the mouth of the bottle would answer just as well. The
end of the wire, projecting above the supporting cork
or cardboard, will serve as a handle for lowering or
raising the cup so as to bring it into or near the
center of the bottle, in the midst of the supply of
Having finished these preparations, Uncle Paul
carefully took up one of the large bottles in reserve,
together with the glass full of water in which it stood
and which served to close its mouth. These, without
disturbing their relative position, he carried to the
bowl, and there, under water, the glass was removed and
replaced by the palm of the hand applied to the
bottle's mouth. In this way it was possible to set the
bottle upright on the table without bringing its
contents into communication with the outside air. A
small sheet of glass laid over the mouth closed the
bottle, serving as it had done before as a temporary
stopper. By means of the iron wire passing through the
cork stopper, the cup, which had previously been filled
with small fragments of sulphur, was so adjusted that
it would take its proper place in the bottle when all
was ready for it. Then Uncle Paul set fire to the
sulphur and lowered the cup containing it into the
oxygen. Thus suspended in the middle of the bottle and
held there by its cork support, the cup of
 sulphur required no further attention on the part of
the experimenter, and there was nothing more to do but
watch the result.
Everyone knows how slowly and with what a dim light
sulphur burns under ordinary conditions. Hence the
novelty of the spectacle now presented to the
astonished gaze of the two young chemists. At their
uncle's bidding the shutters had been closed, so that
no daylight should get in and dim the splendor of the
burning sulphur. It burned with an ardor unapproached
by any brimstone match that was ever made. A fantastic
radiance of a beautiful violet blue, rivaling in purity
the rainbow's purple stripe, emanated from this
wonderful illuminant and filled the room with so
strange a glow that one might have fancied oneself
transported to some other world where the sun is blue.
"Magnificent, magnificent!" cried Emile, clapping his
hands with enthusiasm.
The fume of burning sulphur, escaping in puffs from the
bottle and almost suffocating in their intensely
pungent odor, tended somewhat to spoil this
fairy-like illumination, otherwise so perfect;
and so Uncle Paul, as soon as the flame began to die
down, had the shutters and windows opened.
"It is all over," said he; "the sulphur has used up
its supply of oxygen. I will not dwell on the splendors
you have just witnessed, as your eyes have done better
justice to them than could any words of mine. They have
told you that sulphur burns in oxygen with a heat and a
brillance that it does not have when burning in
ordinary air. I
 will pass on to inquire what has become of the sulphur
we have just seen burning so brightly. What has
resulted from its combination with oxygen? The result
is an invisible gas with a pungent odor, a gas that
makes one cough,—the same gas, in fact, that
comes from a lighted match. A little of it has escaped
into the room—our sense of smell and our coughing
tell us that—but a good deal is still left in the
bottle. Let us consult our tincture of litmus and see
what information it will give us. I pour a little into
the bottle and shake it up, whereupon the blue color
immediately turns red. What does the litmus say?"
"It says that the sulpur has turned into an acid by
burning," replied Jules.
"And it's a good thing it does say so," put in Emile,
"for it would n't have been very pleasant to taste it;
and, besides, you can't even see it. That litmus is
certainly a convenient thing to have around."
"Very convenient," assented his uncle. "Here is
something that can be neither felt nor seen, and yet a
very real thing that takes you by the throat and makes
you cough worse than if you had the
whooping-cough. We wish to know what it is, and
our litmus on being consulted answers: 'It is an
"Does it say, too, that it is sour?"
"Undoubtedly. What reddens litmus and blue flowers, is
"But how to make sure that the litmus and the
 violets tell the truth? I can't stick my tongue down
into the middle of the bottle."
"The invisible gas from the burnt sulphur will mix with
water, and so a good deal of it is absorbed in the
tincture of litmus that I shook up in the bottle. We
know this to be so from the effect it has on the
tincture, which by itself is only water colored by a
tiny particle of matter that has no flavor. Let us
taste this liquid reddened by the intermixture of the
gas, and we shall find out how our invisible gaseous
compound tastes. Wet your finger freely in it without
fear of too large a dose. It takes a good deal to make
any impression on the tongue."
With their uncle to set them an example the boys tasted
the liquid several times to make sure they had its
"Weak vinegar," pronounced Emile, smacking his lips;
"very weak vinegar."
"Weak, if you like, but still vinegar,—that is to
"It's nothing like so strong as phosphoric acid; that
eats away your very flesh."
"Our sense of taste, then, agreeing with the tincture
of litmus, tells us that sulphur by combining with
oxygen in burning becomes an acid. It is this invisible
gas, therefore, that has that pungent odor and makes us
cough; and it is called sulphurous acid."
"You told us," said Jules, "of another acid made from
sulphur, sulphuric acid, which you just used
 to turn the tincture red. Then sulphur makes two acids,
"Yes, my boy, sulphur makes two acids, one with less
oxygen and one with more. The one with less oxygen, and
so the weaker, the less sour, is sulphurous acid; the
other, richer in oxygen and therefore stronger and
sourer, is sulphuric acid. By simply burning, either in
ordinary air or in pure oxygen, sulphur takes on a
certain amount of oxygen and no more, being thus
changed to sulphurous acid; but by roundabout methods
known to chemistry it can be made to take a larger
dose, and in doing so it becomes sulphuric acid. Enough
about sulphur. Let us next see what will be the result
of burning charcoal in oxygen."
A piece of charcoal no bigger than one's little finger
was fastened to one end of an iron wire and the other
end passed through a small disk of cardboard that was
to rest on the mouth of the bottle of oxygen. Uncle
Paul then lighted the charcoal in the flame of a
candle, but only enough to make it glow at one little
point, and in this condition he lowered it into a fresh
bottle of oxygen, conducting the operation in the same
manner as with the sulphur.
The spectacle that followed rivaled in beauty the one
just applauded so enthusiastically by Emile. At the
point kindled by the candle, a spark so faint as to be
hardly visible, a flame burst forth,—bright,
ardent, irresistible,—and, spreading rapidly
through the charcoal, soon turned it into a dazzling
little forge. It gave an intensely white light,
 with little sparks snapping and darting in all
directions, like so many shooting stars shut up in the
bottle. It had taken but an instant to set the charcoal
all aglow in a way impossible with any draft of
ordinary air. Without moving his eyes from this
brilliant spectacle, Emile gave utterance to his
"This heat and this bright light and these sparks I can
make come when I blow with the bellows on burning
charcoal. At the spot just under the nozzle of the
bellows the charcoal burns almost as brightly as this,
here, in the bottle."
"That is quite natural," rejoined his uncle. "With the
bellows you send out air,—that is to say, oxygen
mixed with a good deal of nitrogen, this latter
weakening the effect. But by a sufficiently rapid
renewal of this air that helps things to burn, the
glowing charcoal may be made to brighten up and look
much like this before us in the bottle of pure oxygen."
The supply of oxygen being at last used up, the
unconsumed charcoal turned dimmer and dimmer, and then
quite black. The shutters, which had again been closed,
were reopened to let in the daylight, the previous
admission of which would have greatly lessened the
effect of the spectacle.
"What has become of the charcoal that was burnt up?
That is the problem we must now solve," said Uncle
Paul. "There is left in the bottle an invisible gas
having scarcely any odor; and if we trusted only our
smell and eyesight, we might conclude that the contents
of our bottle had
 not changed in the least. But let us submit these
contents to various tests more decisive than those of
smell and sight, and we shall find that there has been
a decided change. First, it is safe to predict that, if
the charcoal which burned so brilliantly in the
beginning will now no longer burn in the bottle, a
lighted candle will not burn there any better. Watch. I
lower this candle, well alight, into the bottle, and it
is hardly inside the neck before it goes out.
Consequently, there can be no more oxygen left, for if
there were, the candle, as you know, would burn with a
"Still another test: I pour into the bottle a little
tincture of litmus and shake it up thoroughly so as to
give the gas a chance to act on the liquid. The blue
tincture changes its color to a very pale red. Shaken
up with oxygen, the same tincture would not show the
slightest change. Hence, we have here another acid made
by burning something in oxygen. We are now convinced
that the oxygen in the bottle has been converted into
another gas, no less clear, no less invisible, but
endowed with very different properties; and this
difference, it is plain enough, can be due only to the
addition of charcoal (or carbon, which is virtually the
same thing) to the oxygen. Hence we must conclude that
in this gas, here in the bottle,—a gas so
colorless that we cannot see it,—there is at
least some slight quantity of carbon, that substance
known to us as hard and heavy when we see it in coal."
"I see now that it must be so," assented Emile; "but
if any one had told me, without being able to
 prove it, that there was carbon in a gas as invisible
as air, I should n't have been in a hurry to believe
him. What do you say, Jules?"
"I say that it is hard to get used to the idea that a
thing we can't see or feel can have carbon in it. If
Uncle Paul, instead of leading us step by step to where
we are now, had begun by saying that there is carbon in
this bottle in which I can see nothing at all, we
should have looked at him in the greatest astonishment.
But the proofs are there and can't be got rid of. The
charcoal in burning has changed to a gas that turns the
litmus tincture red, and so it must be an acid
called— Uncle has n't told us yet what it is
"Consult your grammar of chemistry, and find the name
"That 's so! I'd forgotten all about that. Charcoal is
the same as carbon, and the ending ic added to
carbon makes carbonic. The gas that comes
from burning charcoal is carbonic acid."
"Is it sour like the others, this carbonic acid?" asked
"Of course, but so slightly that in the gas we have
here in our bottle this acid quality is barely
perceptible. The litmus, instead of turning a decided
red, took on only a faint winy tinge, and to the sense
of taste the sourness would be correspondingly feeble.
But some day an opportunity will occur to convince you
that carbonic acid is indeed sour to the taste. Now let
us put our third bottle of oxygen to its intended use.
In it I propose to burn some iron, a thing that Emile
was inclined to think impossible
 the other day. And I shall make this iron burn without
having to heat it red-hot beforehand in a forge, as
the blacksmith does with his iron before hammering it
into shape. I shall set it on fire with a piece of
lighted tinder, as if it were a train of gunpowder."
"And the iron will catch fire just from that piece of
tinder?" was Emile's wondering inquiry.
"Certainly; gunpowder could n't do it better. Here is
an old watchspring, broken at one end and of no further
use. It is a bit of refuse I got at the clockmaker's.
But instead of this spring, which is admirably suited
to the requirements of our next experiment on account
of its thin flat ribbon-shape, offering plenty of
surface to the action of the oxygen, we could use an
iron wire about as fine as a medium-sized needle,
first cleaning it well with a file or, better, with
sandpaper. The watchspring, however, is to be
preferred. I begin by heating it over some live coals
in order to take away its stiffness and make it supple.
Then I wind it around a slender rod of some
sort—a penholder or a lead-pencil will
do—to give it a spiral or corkscrew form. Next I
take a pair of stout scissors and cut one end of our
corkscrew into a point, which I stick through a bit of
tinder about as large as your finger-nail.
Finally, the other end of the corkscrew is passed
through a small disk of cardboard which will be placed
over the bottle's mouth and will hold the metal ribbon
in position in the midst of the oxygen. The spiral of
our corkscrew should be pulled out to such a length as
to bring its lower end into the middle of the bottle.
If a wire is used instead of a watchspring, the same
 mode of operation should be followed,—the same
winding of the wire into a corkscrew form, the wire
being first heated if necessary and also (an
indispensable detail) cleaned with sandpaper, and the
same use of tinder attached to the lower end of the
All these arrangements being carefully completed, the
third bottle of oxygen was set on the table. In
preparing for it, Uncle Paul had taken care not to fill
this bottle entirely with the gas, but to leave several
inches of water in the bottom.
"There's some water in the bottle," Emile pointed out,
resolved not to let any detail of this curious
experiment escape him.
"Yes, and it is there for a purpose. If there were
none, some would have to be poured in now. A
considerable depth of water at the bottom is necessary
if we wish to keep our bottle for future experiments.
You will very soon see why the water is needed. Close
the shutters and I will begin."
As soon as the room had been darkened, the tinder was
lighted and the spiral ribbon lowered into the oxygen.
The tinder flared up suddenly and burned with a bright
flame. Next followed a moment of indecision; the iron
was taking fire; then it was well on fire and
presented the appearance of a piece of fireworks. This
marvelous flame, feeding on metal, was seen to make its
way upward in a spiral curve as a fire spreads from
bottom to top of a winding staircase. Snappings and
cracklings and sprays of sparks accompanied the
process. At the end of the ribbon there collected and
hung suspended a globule
 of molten metal of dazzling brightness. Growing too
heavy, it detached itself and fell. Still intensely hot
it plunged through the water with a sharp hissing sound
and in a state of redness reached the bottom of the
bottle, which it softened as it flattened itself out
there. Other globules followed, dropping one by one
from the flaming spiral, and despite the cooling effect
of the water the largest ones retained enough heat to
melt the glass a little and sink into it.
The boys stood silent before this magic spectacle of
iron devoured by oxygen; but Emile was not without his
fears. The hissing when the melted globules fell, the
failure of the water to extinguish immediately these
drops of liquid fire, the snapping and spluttering of
the burning watchspring, the showers of sparks and the
cracking of glass, all united to furnish a spectacle of
startling strangeness. Holding his hands before his
face to protect it, the boy was evidently expecting
some terrific explosion. But all ended very quietly,
and only the bottle, cracked in several places,
suffered any damage from this chemical celebration.
Then Uncle Paul broke the silence that had ensued.
"Well, Emile, does iron burn? Are you convinced at
"I shall have to be," he replied. "Iron burns, and it
burns fast. It was like a little show of fireworks."
"And you, Jules,—what do you think of my
"I think it even finer than the one with magnesium.
That metal made a light such as I had never seen before;
but magnesium itself was something
 new to us, and so it could not surprise us very much to
see it burn. With iron the case is different: we are
used to this metal and have so often seen it resist
fire that when we see it burn like wood-shavings
it strikes us both as something wonderful. But what
surprised me most was to see those drops of melted iron
stay red-hot for some moments under water."
"Those globules that fell from the spiral as the flame
ascended are not iron, but oxid of iron, formed by the
combination of that metal with oxygen. I will take out
of the bottle those that are not stuck to the glass.
They consist, you see, of a black substance that
crumbles easily in the fingers. If they were of iron
alone, they would not do this. Their softness points to
the presence of another element, and this element, as I
said, is oxygen. You will find this same oxid of iron
in the tiny scales, black and easily broken, that fly
off when the blacksmith hammers red-hot iron on
his anvil. Both are iron that has been through fire,
iron that has become oxidized. Notice also, on the
inside surface of the bottle, a light layer of fine
reddish dust that was not there before. What can this
red dust be? What soes it look like?"
"It looks a good deal like iron-rust," replied
Jules; "at least it has exactly the color of
"And it is iron-rust,—that and nothing
else. Remember this little fact, for it will be useful
to you later: iron-rust is iron combined with
"Then were there two oxids of iron made in the bottle?"
 "Yes, two, but in very unequal parts. The more abundant
is the black substance; the other is the red dust
deposited on the inner surface of the glass; and this
latter is richer in oxygen than the other. I will not
dwell on this subject further now, as I shall come back
to it later. Notice, finally, the cracks in the bottom
of the bottle and the globules of oxid embedded in the
"Those drops of oxid must have been terribly hot," said
Emile, "to melt the glass like that after going through
water. I've often seen drops of fire fall from the fat
when you singe a roast, but I never knew before that
there could be ever so much hotter ones."
"Was I right, then, to leave some water in the bottle?"
"I should say so! If you hadn't, the bottom would have
been bored clear through."
"More than that; the bottle would have been shattered
to pieces by the sudden intense heat. The first drop to
fall from the ribbon would have ended the experiment by
breaking the bottle. But with this protecting layer of
water our bottle has held together and, although
cracked, can still be used."
There still remained a fourth bottle of oxygen. Also,
safely caged and well supplied with bread crumbs, the
sparrow was watching the proceedings. In the midst of
plenty, captivity did not seem to depress its spirits
unduly. But now its turn had come to be experimented
upon, though without any fatal ending in prospect this
time, Uncle Paul had assured his hearers. The death of
the bird's unlucky
pre-  decessor had shown the boys that nitrogen is
unbreathable, and that in this gas in which a
flame goes out life also is extinguished. What new
truth was this sparrow to teach them? It was about to
show them the effect of oxygen when breathed unmixed
with any other gas. Their uncle took the sparrow and
put it into the remaining bottle of oxygen.
At first nothing unusual occurred. Then, after a short
interval, the saucy bird became even more alert,
brisker in its movements, livelier in every way, than
under natural conditions. Hopping about, flapping its
wings, stamping with its feet, pecking the glass walls
of its prison with furious beak, the little creature
was evidently in a burning fever which was fast using
up its strength. It panted as if its little breast
would burst with the wild pulsations of its heart. Its
open beak denoted extreme fatigue, and yet the feverish
restlessness still increased. To prevent a sad ending
to this scene, Uncle Paul hastened to put the bird back
into its cage, where the fever subsided in a few
"My demonstration is finished," he announced: "oxygen
is a breathable gas; an animal can live in it; which
not the case with nitrogen. But life goes on more
intensely in oxygen than is altogether agreeable, as we
have just seen from the sparrow's extraordinary
"Never before," said Jules, "have I seen a sparrow so
worked up. It acted like one possessed. Why did you
take it out of the bottle so soon?"
 "Because it would have killed the bird to keep it in
there much longer."
"Is oxygen a gas that kills?"
"On the contrary, it give life."
"Well, then, I don't see—"
"Recall the lighted candle that was lowered into
oxygen. It went on burning there, but with a devouring
ardor and an immoderate expenditure of wax. The flame
was of superb brilliance and vigor, but of short
duration. The fuel that would have kept it going a long
time under ordinary conditions was used up in a few
seconds. It is much the same with life; it goes at an
unnatural pace in pure oxygen, uses itself up too
rapidly to last long. We might express it by saying
that the animal machine is geared too high, and hence,
like all over-driven machines, breaks down and
stops. You saw how the bird performed all sorts of mad
antics, as if violently intoxicated. At that rate its
poor little machine would surely have gone to pieces
very soon, and that is why I took the exhausted
creature out of the bottle, wishing to keep it for
another and final experiment. Take good care of it